The present invention relates generally to optical imaging systems, and more particularly to a compact optical imaging system exhibiting a wide field of view (FOV), large exit pupil, large eye relief, or a combination thereof.
Optical systems, while their designs are quite varied, primarily serve to collect radiation from a finite dimensional or angular object to form an image for later use. The goal of optical design is to maximize the fidelity of the image as required for such later use while producing a practical configuration of optical system elements. Generally, a low number of optical elements is desired to minimize cost and system size, while a greater number is desired to offer sufficient design flexibility to minimize optical aberrations and therefore achieve the highest image fidelity. This competitive design environment becomes even more problematic as the desired field of view, exit pupil or eye relief are increased because such increases lead to significantly greater optical aberrations. This in turn increases the number and cost of optical elements required by the imaging system to maintain acceptable image quality.
Many optical imaging systems such as microscopes and telescopes utilize a positive objective lens to produce an intermediate image which is later re-imaged by another positive ocular or eye lens. Unfortunately, the aberrations of multiple positive lenses tend to compound themselves. However, positive lens aberrations are in certain cases opposite in sign compared to the same aberrations in a negative lens. Thus, many imaging systems employ a combination of predominantly positive and less powerful negative lens elements to minimize aberrations. Therefore, since such compounding of lenses requires many more elements, such a technique has only limited utility in systems which must be practically produced with low cost and in compact configurations while also providing a large FOV, exit pupil and/or eye relief.
Further, known imaging systems try to produce a wider field of view by employing a positive field lens at or near the intermediate image. However, such arrangements for widening the field of view are not satisfactory since the field lenses do not serve to make such systems more compact, and they can add significant aberrations to the intermediate image if such lenses are particularly powerful or if there is significant field curvature in the intermediate image.